1. Field of the Invention
The present invention relates to electrostatic-capacitance-type coordinate input devices, which are operated with a user's finger and so on, and in which the coordinate position of a touched portion is detected based on a current variation according to a variation in electrostatic capacitance and the coordinate position of the touched portion is input.
2. Description of the Related Art
In recent years, notebook computers have been widely used for space-saving in offices and homes. In this type of computer, a pad-type coordinate input device operated by dragging a finger on a touch board has been widely adopted and put into practical use as a coordinate input device for moving a cursor displayed on a display.
FIG. 7 is a perspective view showing the configuration of a critical portion of a coordinate input device 100.
The coordinate input device 100 shown in FIG. 7 includes a planar touch board 101 provided at the top, a film substrate 106 comprising a dielectric thin film such as a resin film provided on the lower surface of the touch board 101, and a circuit board 107 provided on the lower surface of the film substrate 106. The film substrate 106 is a dielectric substrate. The upper surface of the film substrate 106 is provided with a plurality of X-electrodes 106a at predetermined intervals and the rear surface thereof is provided with a plurality of Y-electrodes 106 at predetermined intervals. The planar touch board 101 is bonded to the upper surface of the film substrate 106 with an adhesive or the like. Also, the film substrate 106 and the circuit board 107 are bonded via a dielectric film (not shown).
In the above-described film substrate 106, the Y-electrodes 106b extend in the direction orthogonal to the X-electrodes 106a and the electrodes 106a and 106b are arranged in a matrix in plan view, with the film substrate 106 therebetween. Also, the X-electrodes 106a and the Y-electrodes 106b are printed on the upper surface and the lower surface of the film substrate 106 respectively, with a silver paste or the like. Further, through-holes 108 are formed along one edge of the circuit board 107 and along another edge adjacent to that edge. Also, land portions electrically connected to the electrodes 106a and 106b are formed on the rear surface of the film substrate 106 at positions corresponding to first ends of the X-electrodes 106a and first ends of the Y-electrodes 106b. The land portions and the through-holes 108 of the circuit board 107 are electrically connected. That is, the X-electrodes 106a and the Y-electrodes 106b are electrically connected to a wiring pattern formed on the upper surface of the circuit board 107 via the through-holes 108.
Further, a ground layer 109 comprising a copper foil or the like is provided at the center of the upper surface of the circuit board 107. The ground layer 109 helps to prevent a signal generated in the lower part of the circuit board 107 from disturbing the X-electrodes 106a and the Y-electrodes 106b. Also, a control circuit chip 110 is soldered to the wiring pattern on the rear surface of the circuit board 107. By scanning the touch board 101 with a finger so that the finger is in soft contact with the touch board 101, a part of the electric flux lines formed between the X-electrodes 106a and the Y-electrodes 106b of the film substrate 106 is absorbed by the finger, and thus the electric flux lines to the Y-electrodes 106b are reduced so that electrostatic capacitance varies. The control circuit chip 110 converts the variation in the electrostatic capacitance to a variation in an electrical signal and the variation in the electrical signal is converted to a desired coordinate position, whereby the position of the finger on the touch board 101 can be detected.
The coordinate input device 100 having the above described configuration is often mounted in front of a keyboard in a notebook personal computer and can be operated without the user moving his/her hands much away from the home position of the keyboard. However, in many pad-type coordinate input devices, a flat touch board is exposed at the surface of the computer. Thus, a person who is not accustomed to operate a computer is often puzzled by the operation method and this type of coordinate input device does not have excellent ease of use.
Also, when the area of the touch board 101 is greatly reduced, the operability and ease of use of the above-described coordinate input device are reduced. Thus, it is inevitable that the touch board 101 occupies a predetermined space in the operating portion of a notebook personal computer. Therefore, it is difficult to further miniaturize the touch board in a notebook personal computer including the coordinate input device 100. Accordingly, the inventors of the present invention have considered adding another function to the portion occupied by the coordinate input device 100 and have investigated improving the ease of use of the coordinate input device and electronic equipment including the same, and as a result, the present invention has completed.